1. Field of the Invention
This invention relates to methods and systems to create and acoustically manipulate a microbubble.
2. Background Art
Ultrafast lasers allow light to interact with materials in a femtosecond time period, with peak powers many orders of magnitude higher than that of continuous wave light but with low average powers. Interestingly, an optically transparent material that has no linear absorption of incident laser light may have strong nonlinear absorption under high intensity irradiation of a femtosecond pulsed laser. Nonlinear absorption can lead to photodisruption of the material by generating a fast, expanding high-temperature plasma. Measurable secondary affects of the plasma include shock wave emission, temperature increases and microbubble generation. Many applications of ultrafast laser-induced optical breakdown (LIOB) have been developed recently such as micromachining of solid materials, microsurgery of tissues, and high-density optical data storage.
The dominant breakdown attributes studied in liquids are shock wave emission and microbubble generation. As shock waves propagate spherically outward from the laser's focus, they dissipate energy and can be considered broadband pressure waves after propagating only a few wavelengths from the source.
Relatively long wavelength light in the near infrared can penetrate several mm of tissue. High intensity ultrafast pulses (typically several hundred fsec or less in duration) can be focused to internal structures, producing nonlinear photodisruption only in a very small region centered at the focal point of the optical system. Because of the short pulse duration, the total energy per pulse is very small, so there is virtually no damage outside of the photodisruption zone. Such procedures are used for non-invasive eye surgery at the micron scale, as shown in U.S. Pat. No. 6,146,375. Recent results have demonstrated that these methods can be extended to produce nanoincisions without any damage to surrounding tissue.
A concomitant of the photodisruption process is a nanobubble. These bubbles can remain in tissue for a period ranging from several msec to minutes, depending on the mechanical environment.
U.S. Pat. No. 6,391,020 discloses photodisruptive laser nucleation and ultrasonically-driven cavitation of tissues and materials.
“Optical tweezers,” as described in U.S. Pat. Nos. 5,620,857 and 6,416,190, are used to manipulate biological structures such as individual macromolecules and subcellular structures. Optical tweezers require an optically refracting bead, limiting this approach to isolated preparations (i.e., individual molecules or cells or isolate systems).